The primary use of scramblers in Line Coding Schemes is to –

In Line coding, scramblers are used to modify the bit stream before transmission.

A scrambler does not compress or change data content

It randomizes the bit pattern

This helps:

Avoid long runs of 0s or 1s

Improve synchronization

Reduce DC bias in the signal

So the main purpose is to make the signal appear random-like, not predictable.